Former President Bill Clinton has been seen as an asset but also a concern for his wife’s campaign, with aides worrying about his paid speeches, battling his team over his fundraising role, and monitoring what he says in his appearances on the trail, hacked emails posted by WikiLeaks suggest.

The internal messages depict a Hillary Clinton team that is eager to maximize her husband’s value while navigating the pitfalls that surround a two-term president who has a legacy to protect, a complex history and his own ideas on...